﻿using System;
using System.Diagnostics;

namespace SkiaSharp.Views.Blazor.Internal
{
	internal struct ValueStopwatch
	{
		private static readonly double TimestampToTicks = TimeSpan.TicksPerSecond / (double)Stopwatch.Frequency;

		private readonly long _startTimestamp;

		private ValueStopwatch(long startTimestamp)
		{
			_startTimestamp = startTimestamp;
		}

		public bool IsActive => _startTimestamp != 0;

		public static ValueStopwatch StartNew() =>
			new ValueStopwatch(Stopwatch.GetTimestamp());

		public TimeSpan GetElapsedTime()
		{
			// Start timestamp can't be zero in an initialized ValueStopwatch. It would have to be literally the first thing executed when the machine boots to be 0.
			// So it being 0 is a clear indication of default(ValueStopwatch)
			if (!IsActive)
				throw new InvalidOperationException("An uninitialized, or 'default', ValueStopwatch cannot be used to get elapsed time.");

			var end = Stopwatch.GetTimestamp();
			var  timestampDelta = end - _startTimestamp;
			var ticks = (long)(TimestampToTicks * timestampDelta);
			return new TimeSpan(ticks);
		}
	}
}
